Subject: Re: CCL:Final structure in terms of initial Z-matrix

From: TREVOR D POWER <[email-masked]>
Date: Sun, 17 Dec 2000 13:42:26 -0600 (CST)

Namazian,
	What version of Gaussian are you using?  94?  Are you employing
dummy atoms in the construction of you input file?  I am not really sure
what "Final structure in terms of initial Z-matrix" implies.  If you
specify a geometry in the input.file as a Z-matrix in either Gaussian 94
or Gaussian 98 without using opt=z-matrix the input geometry with be
converted to redundant internal coordinates and the output parameters of
the optimized geometry will not necessarily correspond to those in the
input z-matrix.  By default, Gaussian 92 interpreted opt (in the route
card) as opt=z-matrix.  You should note that opt=z-matrix is a very poor
manner in which to obtain an optimized geometry because 1) the program
will take forever to optimize the geometry based on just those parameters
you specify in the input.file and 2) you have a very good chance of
obtaining a local minumum as a result of inherent constrainst this
technique employs.  
	What I would do is specify opt=addredun (Gaussian 94) or
opt=modredun (Gaussian 98) and at the end of the geometry input section of
the input file explicity list those redundant coordinates you wish to see
(in addition to those the program selects) in the output file.  You will,
of course, need to know what the approximate values are for these
parameters so as to not perturb your initial geometry too much:

1 2 1.43     (for bond length)
1 2 3 120.0  (for angle)
1 2 3 4 34.0 (for dihedral angle)

where 1, 2, 3 and 4 are atoms specified.  If you use dummy atoms in the
input, you cannot use these to construct these coordinates as dummy atoms
are deleted once the geometry is read into the program and the molecule is
transulated into redundant internal coordinates.
	You can get additional bond lengths from the distance matrix in
the output.file.  Also there is a way to print all angles and all
dihedrals.  If you are interested in that I can dig this up later.

Hope this helped,
David Power
Department of Chemistry
Univerity of North Texas
NT Staion, Box 305070
Denton, Texas 76203-5070
[email-masked]

On Sat, 16 Dec 2000, Mansoor Namazian wrote:

> Dear Sir,
> 
> When I optimize a molecule using Gaussian, sometimes I get
> the "Final structure in terms of initial Z-matrix:" at the
> end of output file and sometimes I don't, no matter what
> I specify in the route section.
> I'd like to get always "Final structure in terms of initial
> Z-matrix" at the end of output file. Can anyone help please?
> 
> Many thanks in advance.
> Namazian
> 
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